BUG #7832: incorrect summation of ipv6 addresses

The following bug has been logged on the website:

Bug reference:      7832
Logged by:          George Shuklin
Email address:      shuklin@selectel.ru
PostgreSQL version: 9.1.0
Operating system:   GNU/Debian Linux Wheezy
Description:        =


Normal summation:

 SELECT cidr'0::1/128'+1;
 ?column? =

----------
 ::2



SELECT cidr'0::1/128'+65535;
 ?column?  =

-----------
 ::0.1.0.0

(strange dots in the middle of the ipv6 address).